The invention relates to a liquid filter, particularly for oil or fuel of an internal combustion engine with a substantially cylindrical housing and a sealable oil drain.
Such filters are known, for instance, from DE 196 06 616. They comprise a substantially cylindrical filter housing, wherein the replaceable filter cartridge is accommodated in a housing base onto which a screw-on cover is placed. A problem occurs, however, when the filter cartridge is replaced, particularly in horizontally installed filters, because there is an oil residue in the housing. To prevent said oil residue from running out of the housing as the cartridge is being replaced, a return flow channel is provided on the housing base to ensure the return flow of the residual oil from the housing through a special opening in the crankcase of the internal combustion engine.
The disadvantage of this type of construction is that a corresponding return flow opening must be provided in the crankcase. As a result, it is not possible to retrofit engines originally designed for a disposable filter with a liquid filter of this type, since these engines do not have such an opening.
To provide the advantages of greater economic efficiency and environmental compatibility in these older engines as well, EP 0 692 292 proposes a liquid filter in which a sealable drain opening is provided in the housing base. To ensure that this drain opening is located at the lowest point of the filter housing even if the housing is horizontally mounted, the filter is not screwed directly into the connecting piece provided therefor, but is held in the mounting location by a sleeve provided with screw threads. The disadvantage of this type of construction becomes evident in the initial mounting of the filter. The filter must be provided at the mounting location in its individual parts, since the threaded sleeve is accessible only if the housing base is open. This makes final assembly considerably more difficult. In addition, there is a risk that sensitive individual parts, particularly the filter insert, may be damaged, which would affect the quality of the product.
Thus, it is the object of the invention to create a liquid filter with a replaceable cartridge, which can be used in place of ordinary disposable filters, which may be mounted as a preassembled unit during initial installation, and which ensures reliable drainage of the oil located in the interior of the housing when the filter cartridge is replaced. Said liquid filter is provided for mounting positions with a substantially horizontal center axis or with a housing cover pointing in downward direction.
This object is attained by the invention as described and claimed hereinafter.
The liquid filter according to the invention comprises a substantially cylindrical housing, which is formed by a housing base and a screw-on cover. The housing base is provided with an inlet and an outlet for the fluid to be filtered and is positioned at the mounting location in such a way that its passages communicate with the corresponding openings in the mounting location. A threaded socket, in particular, is provided for this purpose, which is used to screw on the liquid filter. This connection simultaneously provides the outlet. The housing base is provided with a thread along its outer wall by means of which it can be screwed together with the threaded cover. This screwed connection is sealed, for example, by an O-ring. The housing base and screw-on cover together form the holder for the filter cartridge, which is arranged in the housing in such a way that the fluid to be filtered flows through the filter cartridge. In addition, an oil drain is provided in the screw-on cover, which is located in the area of the outer circumference of said screw-on cover. This may be in the area of the cylinder jacket of the screw-on cover or at the edge of its lid area.
When the housing base is screwed onto the threaded socket to mount the liquid filter in the mounting location, the angular position of the liquid filter in relation to its center axis cannot be predicted. The same is true for the oil drain. As a result, for instance if the liquid filter has a horizontal center axis when mounted, the oil drain may not be located at the lowest point of the housing interior. To make it possible nevertheless to drain the residual oil completely from the filter housing prior to replacing the filter cartridge, the screw-on cover can be loosened and subsequently rotated far enough so that the oil drain is located at the lowest point of the housing volume. This simultaneously causes an axial displacement of the screw-on cover within the housing base. To ensure, nevertheless, a reliable seal of the screwed connection between screw-on cover and housing base, sealing means are provided, which guaranty a seal between the housing parts in the area of said axial displacement. This may be accomplished, for instance, by an O-ring, which slides a distance along a sealing surface when the screw-on cover is opened. Said O-ring can simultaneously perform the sealing function when the oil filter is in operation, or a separate seal may be provided for this purpose.
The liquid filter according to the invention is suitable not only for mounting in horizontal position. It can also be installed with its screw-on cover pointing in downward direction. Depending on the mounting position, some residual oil may remain within the filter housing even after the remaining oil has been drained, but this will not interfere with cartridge replacement. This is true particularly for a mounting position in which the screw-on cover points in a slightly upward direction.
According to an advantageous further embodiment of the inventive concept, a sealable vent is provided on the housing in addition to the oil drain. This vent is preferably located in an area opposite the oil drain. When the screw-on cover is rotated, the oil drain thus travels to a lower area of the housing and the vent to a higher area. When the oil drain is opened, air can then flow through the vent into the housing to accelerate the draining process.
In an advantageous variant of the invention, the oil drain is provided with a drain plug. This is a simple component and thus contributes to the economic efficiency of the liquid filter.
A further variant of the invention provides that oil drainage and/or venting be ensured by channels running through the walls of the housing part. Said channels must be made in such a way that they are sealed by the mounted screw-on cover. If the oil is to be drained, the screw-on cover is rotated far enough that the channels are unblocked and one channel is located at the lowest point of the housing. The oil flows out of the housing through said channel. If a second channel is provided, located opposite the first one, that second channel is used as a vent.
A special embodiment of the invention uses as a channel the gaps created between the housing base and the screw-on cover as a result of the thread geometry. As soon as the sealing means unblock the path toward the outside, the oil can flow out of the housing through the thread passages, and air from the outside can flow into the housing. Advantageously, the thread selected is a saw-tooth thread, since this type of thread has large enough gaps in the turns to carry the oil. In addition, the thread can advantageously have an axial recess, which widens the cross-section of the channels. Said recess may consist of a flattening of the thread on the screw-on cover, or of a groove.